Push-pull resistance type phonograph pickup



March 25, 1952 J. H. MCKNIGHT PUSH-PULL RESISTANCE TYPE PHONOGRAPH PICKUP Fled May 12, 194s 3 Sheets-Sheet 1 March 25, 1952 J. H. MGKNIGHT PUSH-PULL RESISTNCE TYPE PHONOGRAPH PICKUP 3 Sheets-Sheet 2 Filed May 12, 1948 4h; www

March Z5, 1952 J. H. MCKNIGHT 2,590,439

PUSH-PULL RESISTANCE TYPE PHONOGRAPH PICKUP I Filed May 12, 1948 5 Sheets-Sheet 5 /v m @WNW Patented Mar. 25, 1952 PUSH-PULL RESISTANCE TYPE PHONOGRAPH PICKUP Joseph H. McKnight, tov Star Electronics, I

sylvania Pittsburgh, Pa., assigner ne., a corporation of Penn- Application May 12, 1948, Serial No. 26,511

18 Claims.

This invention relates to pick-up or to converter pick-up devices and to apparatus arrangements for sound reproduction, and particularly, to new and improved apparatus and procedure for audible translation or reproduction of sound tracery of a track, record, tape, etc.

At the present time, the phonograph and allied industries, although highly developed in many respects, have encountered considerable difficulty in providing suitable apparatus for picking-up sound record tracery and faithfully reproducing it in the form of audible sound waves. The socalled crystal type ofpick-up has been generally adopted, after many unsuccessful attempts along other lines, and in spite of the fact that such a type of pick-up has inherently disadvantageous characteristics and operative limitations.

Although the industry and those skilled in the art have for many years been experimenting to nd some other suitable and better form of pickup for this purpose and attempts have been made to utilize carbon disks and carbon granules, no one has been able to develop an inexpensive, high fidelity, practical type of pick-up to take the place of the crystal type.

In spite of the discouraging results heretofore obtained lby those skilled in the art, I set out to solve the problem involved, with the conviction that they had in some manner overlooked some controlling factor or factors in their approach. In my experimental work, I determined that a resistance type of pick-up should provide new and improved results if some method could be found to successfully employ it. Such a type of pick-up can be employed as a current convertor, as distinguished from a current generator, by applying an electrical voltage across it, and by effectively varying current flow in wave form in accordance with variations in a record tracery.

I determined that prior attempts hadbeen unsuccessful because those skilled in the art had made a wrong approach to the construction and actuation of such a type of pick-up; that the key to success rested upon a proper approach to factors involved in converting needle or follower variations into electrical resistance variations. After many unsuccessful attempts, I finally reached a solution to the problem that not only has the advantageous features of a crystal pickup without its attendant disadvantageous features, but also, that has new and improved features.

It has been an objejct of my invention to provide a new and improved form of reproducing arrangement or pick-up;

Another object has been to find a solution to the problem heretofore presented in the art;

Another object has been to provide a lpick-up or reproducer that will provide a suitable wattage output such that a speaker may, if desired, be directly coupled or connected thereto without intermediate amplification;

A further' object has been to broaden the field of sound reproduction by providing a new and improved type of pick-up device, as well as to provide suitable apparatus or circuit arrangements for use in connection therewith;

These and many other objects of my invention will appear to those skilled 'in the art from the disclosure thereof.

In the drawings:

Figure 1 is a side fragmental view in elevation showing how a pick-up device of my invention may be employed with conventional parts of a phonograph;

Figure 2 is an enlarged vertical front view in section through a form of device employing my invention; this view shows a simple circuit diagram or arrangement that may be used with the device;

Figure 2A is a greatly enlarged fragmental section of the device of Figure 2, showing details of the mounting structure; for clarity, the resistance particles are omitted in this view;

Figure 3 is an enlarged vertical side sectional view taken along the'line III-HI of Figure 2;

Figure 4 is a fragmental front detail taken along the line IV-IV of Figure 3;

Figure 5 is a bottom view taken along the line V-V of Figure 2;

Figure 6 is a front, vertical section, similar to that of Figure 2, but showing a preferred embodiment of my invention;

Figure 7 is a vertical side sectional view taken along the line VII-VII of Figure 6;

Figure '7A is a side detail in elevation showing a yoke arrangement employed in the embodiment of my invention shown in Figures 6 and 7;

Figure 8 is a bottom .view taken along thezline VIII-VIII of Figure 6;

Figure 9 is a somewhat diagrammatic view of a simple circuit arrangement employing a pick-up device of my invention and illustrates the device in a normal, starting, or neutral position;

Figures 10 and 11 are similar to Figure 9, but show the direction of current flow when a device of my invention is actuated by an oscillating arm or member; in Figure 10, movement is towards the left, While in Figure 11 movement is towards the right. In this manner, pressure-sensitive conductive portions, granules or particles in opposite microphone halves of the device are compressed to decrease their electrical resistance and to vary and reverse the direction of current flow;

Figure 12 is an enlarged view showing a typical sound tracery on a record and Figure 13 is a diminished chart plotted between frequency and voltage, showing that proportionate alternating current variations may be produced;

Figures 14 and 15 are diagrammatic views showing `typical circuit or apparatus arrangements that may be employed in utilizing my invention; Figure 14 shows the utilization of a center-tapped voice coil of a speaker; and, Figure 15 shows the employment of a center-tapped transformer;

Figure 16 is a, side section in elevation through a speaker provided with a center-tapped voice coil for utilization in a circuit such as shown in Figure 14;

Figure 17 is a front sectional view taken along the line XV II-XVII of Figure 16;

Figure 18 is a View similar to Figure 2 illustrating another embodiment of my invention and further emphasizing an important principle involved therein;

Figure 19 is a side section in elevation taken along the line XIX-XIX of Figure 18.

In accordance with my invention, sound track variations may be properly converted into or reproduced as an electrical current flow of a suitably corresponding Wave form. Summarized briefly, I impress a direct current source of voltage across an electric resistance through an output impedance, e. g. the coil of a speaker or transformer; provide the resistance with selfreturning, self centering, pressure applying means for varying its effective value from at least one side thereof; provide a sound trackactuated oscillator arm; provide a response control means (buifer or frequency cut-off means) between the pressure-applying means and the oscillator arm; and, pressure-position the oscillator arm against the response control means in such a manner that the effective value of such resistance will be properly varied with variations in tracery of the sound track.

It is important that the means for varying the resistance should have an oscillator-armpressure-actuated electric contact portion that is free to and is capable of being urged to return to its starting, neutral, or high resistance-providing position, independently of the oscillator arm, when the arm is free to or is being moved by the record tracery in an opposite direction. In accomplishing this, I may employ at least one, and preferably two, oppositely-positioned resistance or microphone button halves or parts,

each of which contains substantially looselypositioned, pressure-sensitive conductive portions, particles, or granules, e. g., carbon granules, of substantially fine, dust-like, or microscopic size; and, I provide each part with a quick-return diaphragm (pressure-applying means) having a centrally-located, variable-position, pressure-sensitive, electric contact portion.

Each diaphragm is constructed of flexible material or is provided with flexible means for normally urging it away from the conductive portions or particles and towards a minimum-compressing, starting, centrally-aligned, neutral, or normal position. It is important to provide means having an inherent tendency to quickly and positively return, without hunting the electric contact portion of the diaphragm. The electric contact portion of the diaphragm is in substantial axial alignment with a relatively rigid, back wall electric contact portion and is adapted to move with respect thereto to vary current flow therebetween through an interposed layer of the pressure-sensitive conductive portions or particles.

The electric contact portion of the diaphragm is actuated through a pressure contact by a needle-chuck or oscillator arm that is journaled or fulcrumed (preferably in resilient bushings) to freely oscillate in accordance with needle vibrations without extraneous noise generation or pick-up and full sensitiveness and minimum mechanical resistance.

In the illustrated embodiments, opposite, flat Y or planar faces of an upper or transmitting end portion of the oscillator arm have a somewhat exibly-variable pressure contact through response control means with hammer extension portions or studs that project from the diaphragms in substantial axial alignment with their electric contact portions. The response control means may be an interposed flexiblycompressible, fabricated material, such as a moisture-resistant fabric. This response control means is a dampening buffer of a comparatively soft material that has the physical characteristics of a solid (has a definite shape and offers resistance to a deforming force and whose constituent molecules can only vibrate about fixed mean positions), as distinguished from a gas.

The needle-chuck or oscillator arm is shown constructed and arranged to impart such vibrations by pressure contact to oppositely-positioned spaced-apart sensitive diaphragms, whereby the electric contact portions of the diaphragms are periodically moved toward the compressible conductive portions of a two-part resistance, as represented by two oppositely-positioned microphone or resistance halves, and from a starting, neutral, or radially-centered position. That is, as shown, each diaphragm electric contact portion is periodically moved inwardly towards the conductive portions by the oscillator to compress them against aA substantially axiallyaligned electric contact in accordance with variations in the sound record and is free to and does guickly move in an opposite direction toward the oscillator by reason of an inherent force that is independent of the oscillator. The effective distance of such opposite movement, the maximum distance being the diaphragm noncompressed position, is limited by the recordtracery-governed position of the oscillator at a particular moment. The oscillation thus imparted to the diaphragm of a resistance half is then converted into a variation of current flow by a change in electrical resistance of the compressible conductive particles, as eifected by the degree of compression or contact pressure exerted substantially axially across the resistance half (button).

The response control means (buffer) is an important factor in carrying out my invention. In

general. it is employed toproportion the volume ofhighfand low frequency notes to eliminate extraneous and undesirable noises, and to provide a soft, non-scratching, and substantially uniform volume reproduction over the frequency range. That is, it can be employed to decrease the volume of low frequency notes and to lower the volume of high frequency notes of the record tracery. In this connection, I prefer to employ a moisture proof, or a moisture-proofed fabric of' a somewhat flexible material, such as silk, rayon, glass or paperber, cotton, nylon, or a mixture of them. Rubber or cork material can also be used and are suitable for impregnation of other materials, such as'those listed. In general, a` fabricated material ofl cork, plastic, or natural fibers may be employed that will not set"y under a slightv amount of heat or a slight amount of heat and some moisture. For example,l` a water-proofed wool plush of about 0.030" thickness having one side provided with tufts is highly satisfactory. Such tufts or hair like portions aid in curving of response to approach that of the record tracery, in that they have a preliminary resistance to bending under compression force. The tufted side of such a materialis preferably positioned in contact with the oscillator arm and its other or matted side in contact with the pressure-applying means or diaphragm. A softer, pliable material may be employed to give a high frequency cut-off of about 4,000 cycles, and a slightly harder material of about, 6,000 cycles, ete.

Record tracery is based on a curved response andthe ears are more suited to such a type. It is thus important to provide the pick-up or reproducer with such a type of response, as compared to a normally flat response. For example, a suitable response control means may provide a low frequency cut-off of, for example, about 4,000 cycles` (high) and about 60 cycles (low). The response control or dampening means or buffer should be capable of transmitting higher volume notes, but of dampening out, screening out, or absorbing relatively lower volume extraneous noises; it should be of sufcient size or. mass, such that thev material will not become set in one spot or be too soft in its response control. Thus, I prefer to employ a relatively flat contactbetween the oscillator arm, the frequency response control means, and the diaphragm,(pressure-applying means). If desired, the, buffer material may be cemented in position on,-v the .V oscillator arm.

In. the illustrated embodiments of my invention shownV inthe drawings, I show preferred arrangements wherein a pair of opposed resistance elements or button halves are employed. The vibrator-actuator means, needle chuck, or osc'illator arm is mounted within spacing between theresistance elements for free and unharnpered movement' along its length. At or adjacent its upper end, it is positioned centrally between oppositely-extending hammer portions or elements ofy theV diaphragms, to slightly compress the diaphragms when in its neutral or center position, and to provide an operating pressure relationship therewith. The hammer elements or portionsr have what may be termed a slide mounting with respect to the oscillator arm in the sense that they are not rigidly secured thereto, and that the diaphragms are not positively governed in their return movements by the oscillator arm, itself. The diaphragms may be made of flexible, spring-like metalsuchas phosphorus bronze.

Each hammer portionspreferably offmetal and:

may be secured within thecentrally ofset'portion of its diaphragm by sweating, brazing, etc., to make it an integral part thereof. The enclosing walls of each button half are constructed to seal off its contents, to insure maximum efficiency of operation, and to prevent packing of the. conductive particles, and particularly, adjacent its current-flow transverse axis.

By employing a pair of resistance elements or button halves or portions, I may provide an alternating current, sound-representing wave form by utilizing a direct current source of energy. In employing a device of my invention, a circuit arrangement may be utilized in which the conductive portions or particles of a pair of button parts are connected in series with each other to provide an electric resistance; their diaphragm electric contact portions are connected together to provide a two-way variable resistance arm. The oscillator arm or needle chuck is operably positioned to vary the resistance on opposite sides of the resistance in accordance with sound track variations of the tracery of the record or tape by alternately compressing the relativelyloose, conducting portions, particles, or granules to thereby alternately cause a corresponding current flow through the halves of the resistance, and at a denite frequency. Such current varations may be directly imposed upon the voice coil winding of a permanent magnet speaker Without further amplification. The current consumption is relatively low, as compared to a flashlight, for example, and for this reason, ordinary dry cell batteries may be used. A switch may be used to disconnect the batteries when the device is not in use. I have been able to effectively reproduce frequencies fully within the useful audible range of about 50 to 10,000 cycles which considerably broadens the range over an ordinary crystal pick-up.

Referring particularly to Figure 1 of the drawings, I have shown a phonograph l0 provided with a motor and gear box H, a motor I2 and a speed-reducing gearing i3 which actuates a friction wheel i4. A turn-table l5 is rotated by the friction Wheel M. The turn-table I5 is adapted to carry a sound track record VI which is centered thereon by a pin it. A tone arm I0 is pivotally mounted on the phonograph I0 by a bracket i3 and is shown carrying a pick-up device 20 of my invention provided with a suitable record-tracery-following needle N.

In. the embodiment of my invention shown in Figures 2 to 5, inclusive, the pick-up device 20 has a casing or housing for supporting and positioning a spaced pair of opposed current-control buttons, button halves, or resistance elements B and B'. The buttons B and B' are actuated by an oscillator arm C which also carries the needle N. The casing is shown as comprising a pair of vertically or upwardly-extending, oppositely-positioned and spaced-apart side wall portions 2id and 2lb, an integrally connected bottom wall portion 22, and a front wall or cross-piece portion 23 that extends between the side wall portions 2id. and 2lb. The casing or housing, as shown, may be mounted on the tone arm I0 by a setscrew 25 that extends through an inclined front wall portion of the tone arm and that threadably engages a threaded hole 24 in the cross piece portion 23. In this manner,l the de vice 20 may be removably secured. on a suitable tone arm such as I 9.

Press ure sensitive. conductive portionw or.v par.-

ticles 30, preferably carbon granules of the button B are retained by a iront or diaphragm wall portion 3| and a back or supporting wall portion 32. The front or diaphragm wall 3| of a suitable material, such as phosphorus bronze, is positioned to abut against a front ledge portion of a conductive, circular retaining housing 33 and is shown in electrical contact therewith. The back wall portion 32, also preferably of metal or conductive construction, is of smaller peripheral extent than the inner bore of the housing 33, and is further prevented from electrically-contacting such bore by a pair of fiber or non-conducting washers 34a and 3412, see Figure 2A. The front washer 34a is interposed between a back edge or rim portion of the diaphragm 3| and a front edge or rim portion of the back or diaphragm 32, while the washer 34h is interposed'between a back edge or rim portion of the wall 32, and another insulating or non-conducting washer 34e. The washer, diaphragm, and back wall assembly is held tightly in position within the housing 33 by a circular ring 35 provided with male threads about its outer periphery that engage female threads about the inner periphery of the back end portion of the housing 33. rIhe back faces of the buttons B and B' are shown mounted within outer housing or casing side wall portions 2|a and 2lb by suitable circular compression washers 36 and 36 whose transverse faces are widened at the bottom, in order that such washers may rest upon the bottom wall portion 22 of the housing, see Figure 2.

The oscillating element, chuck, or arm C is positioned to extend substantially at right angles to the axis of actuation of the button halves B and B' and is pivoted or iulcrumed on the device 2li to support a needle N and to actuate hammer portions 40 and ll. The hammer portions, as shown, have convexly-rounded ends positioned to engage and rest within inwardlyconcave, offset, or bulging central (electric contact) portions of opposite diaphragm walls 3i and 3| of buttons B and B. It will be noted that the outwardly-concave electric Contact portions of the diaphragme 3| and 3| are located substantially axially-centrally of the buttons and that each of the back walls 32 and 32 of the buttons B and B have a similar, backwardlyconvex, oiiset, or bulging and inwardly-concave electric contact, such that substantially a uniform thickness of granule compartment is provided along the full extent of the spacing between the offset, electric contact portions of the diaphragm and the back wall of each button. The rounded shape of the contact portions also prevents packing of the conductive particles. It will also be noted that the diaphragm 3| has a circular ridge or bead annular 3m, which with its general contour and iiexible metal construction provides it with requisite position-returning characteristics. It will be noted that the diaphragm 3| and 3| is actually flexed by the radial portions thereof that terminate in the centrally-located, offset, electric contact portion. Such electric contact portion is, itself, held somewhat rigidly against the hammer portion 4G and 40 that is carried thereby. The ratio of the space between the electric contact portions of the diaphragm 3| and the back wall 32 is relatively low with respect to the diameter or radial extent of the particle chamber, for example, to Tse".

The needle chuck or stylus holder for the oscillator arm C, as shown, has a downwardly-projecting nose portion 4| and a needle-receiving bore 42 that extends upwardly from the nose portion 4I and terminates in a transversely-extending open-end sight bore 42a.. A bearing or fulcrum shaft portion 43 extends transversely-forwardly and backwardly from the needle chuck C and has opposite-end bearing surfaces that pivotally fulcrum it between a spaced pair of centrallylocated, semi-circular, transversely-extending bearing portions 25a and 2Gb of the bottom wall portion 22 of the housing and similar portions 28a and 28h of a bottom mounting bracket piece or member 21, see Figure 3. Gaskets 44a and 44h of a suitable dampening or resilient material, such as rubber, are positioned between the abovementioned bearing portions and the bearing surfaces of the shaft portion 43 to dampen the oscillator and prevent the pick-up of extraneous noises. As shown, the fulcrum point is nearer the lower end of the arm C and thus provides an oscillation-amplifying action to the upper end thereof. The mounting bracket member 21 is removably secured to the bottom wall 22 of the pick-up housing by setscrews 28, see Figures 2 and 5, which are mounted within internallythreaded holes 29 in the bottom wall. TheV mounting bracket 21 has a central opening21a therethrough of a size suicient to permit free oscillation of the nose portion 4| of the oscillator arm that extends therethrough.

The shaft portion 43 of the chuck C is provided at its front end with a transversely-extending, internally-threaded bore 44 which is adapted to receive a needle-clamping thumb screw 45. The thumb screw 45 is adapted to abut against a side of the needle N and hold to it in a suitably adjusted position within the bore 42. Extending upwardly from the portion 43 is a rounded-shoulder, central portion 46 and a hammer-pressing, flat or planar face, reduced portion 41. Hammer element portions 40 and 40 are adapted to rest upon opposite flat faces of a hammer pressing portion 41 through a response control or buier 48. The buier 48 is, as previously pointed out, of a suitable dampening or sound proportioning material. In addition to providing movement transmission without extraneous sound transmission, it also is preferably flexible enough to absorb the rub of a slight pivot movement between the hammer portions 40 and 40 and oscillator arm C.

In Figures 6 and 8, I have showna preferred embodiment of my invention which is somewhat similar in general construction to the embodi ment of Figure 2. In this embodiment, I have shown the same type of button halves B and B', but they are mounted in a modied form of retaining outer casing or housing. This casing is made up of two similar halves or portions 50 and 5t that may be of die cast metal. Each housing half, such as 50, may be provided with a circular opening or more therethrough and an enlarged bore 5| having an inner periphery of a diameter substantially corresponding to the diameter of the outer periphery of theY button half B, in order that the button half B may be mounted therein by pushing and sliding it from the open, back end of the bore 5| up against a front rim or ledge portion 52. If desired, the ledge portion 52 may be located adjacent the opposite end of the housing 50 and the button B introduced from its other end. The buttons B and B may be secured in their mounted relationship within the bores 5| and 5|' by swedging or pushing-out lug portions 53 from. side walls of the bores. It will be noted that the two lon/e. .of .needle is not so .necessary when the yoke ele- Ahousing parts or halves 50 and 50 are adapted to be positioned with their corresponding inner walls in abutment witheach other and may be held in such a mounted relationship by a series of eyelets 54 that extend through transverse holes 55 and 55', as shown particularly in Figure 6, are preferably enlarged to receive heads of the eyelets 54 in an inset relationship. Outer edges `of the housing halves 59 and 5U' are shown in an abutting relationship with side wall portions of the tone arm I9, although if desired, washers may be interposed therebetween, see the washers 36 and 36 of the embodiment of Figure 2.

Other portions of this embodiment, such as the needle chuck or oscillator arm C as Well as its mounting portions are substantially the same as described in connection with the embodiment of Figure 2. However, as shown in Figure 7A, I have provided a yoke element 63 of a suitable, flexibly-rigid material, such as phosphorus bronze. This yoke, like the buier 48, may be termed a dampening means. As shown in Figures 6 and 7 the yoke 6i) is provided with a lower end portion 6! `that is adapted to be clamped within a vertical slit or slot 41a within the portion 41 of the arm C', see Figure 6. The slit extends downwardly from an upper end of the hammer mounting portion 41 of the oscillator arm C. The lower end portion 6l is connected by'a neck or reduced width portion 62 to a fork portion 63 which is adapted to nt between opposite upper wall faces ofthe two housing halves "56 and 58', see vFigures 6, 7, and 7A. The yoke element 6B is supported in position by the clamping action of opposite facesof the housing halves `i) and 5E and is, in addition, provided with oppositely-extending feet 64 and 65 that rest upon upper or top faces of the housing halves. That is, one foot portion 64 rests upon the top of the housing 5U and the other foot portion 65 rests upon the top of the housing 50'.

The yoke element 6i] serves in a dual capacity. In the rst place, it acts as a spring to normally urge the oscillating arm C towards a neutral or central position (self-centering action); and, in v the second place, it serves as a response control within .certain frequency ranges, for example, to eliminate undesirable highs and low rumbles. The yoke element 6D may be constructed to provide any desired range of frequency response of the pick-up, and to limit extraneous sound response, such as produced by a piece of dirt on the sound record or tape. That is, it may be provided with a tensile strength such that desirable highs may be included by greatly speeding up lthe'return to zero or neutral position, and that at the saine time response to extraneous surface Anoises'will be limited; it acts as a dissipator or radiator of surface noises. It can Vbe provided with suiicient tension to supplement the return action of the diaphragme 31 and 3l. The tapered neck portion 82 is particularly important in providing the desired fiexibility. Ordinarily, I prefer to adjust the force action of the yoke element d using different metal strip thicknesses in fabricating it or by changing the Yneck size. The yoke and the buffer dS are two importanL features and may be employed to supor complement somewhat each other, aithou the buffer i3 or its equivalent is of essential importance.

Although, heretofore, it has been customary to design special types of needles or cam-fol- .for improving reproduction, such a type ment 'EQ is employed. That is, an ordinary straight needle of rather rigid construction N can now be used Without the reproduction of needle scratches and noises.

In Figure 9, I have shown a somewhat diagrammatic circuit layout. In this figure, the buttons B and B and the oscillator arm C has moved to the left to compress the diaphragm 3l of the left-hand button B, thus decreasing the effective resistance thereof, and providing current ow in the direction indicated by the arrows. In Figure 1l, the arm C has moved to the right to compress the diaphragm 3| of the right-hand button B and to provide current flow in the direction indicated by the arrows. In these gures, A1 and .A2 represent suitable batteries which are center tapped at e and are connected to one side `d of the voice coil of a permanent magnet speaker PM. The other side c of the voice coil is electrically connected at b to both of the diaphragms 2| and 2 I of the buttons B and B'. The other ends of the batteries are connected to the back walls of the respective buttons through contacts a and a. As shown in Figure 2, the diaphragms 3| and 3| are in electrical contact with their housings, and thus, the connectionvb may be made directly to such housings. The contacts a and a and b may be made by applying a thin gold spatter to corresponding metal parts of the buttons B and B', as is well known in the art. A double pole switch SW may be employed to disconnect the batteries when the pick-up is not in use.

By employing two opposed buttons, connected as shown, I have been able to produce an audio frequency current of sufcient strength to di-` rectly energize a voice coil of a permanent magnet speaker. I obtain surprising Volume with high fidelity and clarity of reproduction. As an example, the voice coil may be about 8 ohms impedance, and the buttons may be about 40 to ohms each. Employing buttons of about 100 ohms each, I have obtained 3.2 watts output with a 800 milliampere current and 1.8 watts output with a 400 milliampere current.

In Figures l2 and 13, I have illustrated how reproduction that may be attained by employing my invention. Figure l2 is an enlarged sound record tracery curve and Figure 13 is a reproduced electrical curve shown in a diminished scale for better comparison.

In Figure 14, I have shown another type of circuit arrangement wherein a center-tapped speaker is employed, instead of a center-tapped battery. In this arrangement, the battery Aa is connected at one end to a center tap f of the voice cciland at its other end to the pick-up contact b.

v`Figures 1S and 17 show the construction of a suitable center-tapped speaker 'l0 that may be used in this connection. In all of the illustrated circuits a full wave `speaker action may be obtained.

In Figure l5, I have provided anothercircuit arrangement employing va transformer T provided with a primary P and a secondary S. The transformer T may have a 40 to 100 ohms centertapped primary P and a voice-coil-matching:secondary S for better control. The battery A3 is connected between the center tap f and the contact b of the pick-up. The ends h and :i of the transformer primary P are connected to the pickup contacts a and a. The output leads c and d from the secondary S of the transformer T may be connected to the voice coil of a speaker, or in any other suitable manner.

Referring particularly to Figures 16 and 17,the

speaker shown has a permanent magnet 1 I, magnetic .metal pole pieces 12 which provide a coilreceiving hollow center 13, a magnetic metal core 19, a spider 14 securely mounted on front ends of the pole pieces 12, a diaphragm 15 mounted between the spider, and a coil support or form 16. A speaker cone 11 is also mounted on the front end oi' the form 16 and extends outwardly therefrom. A coil 18 is wound on the support from 15 and is provided with taps c and d as well as a center tap f As shown particularly in Figure 17, the pole ,pieces 12 have a groove 12a, extending outwardly from their hollow center 13 to provide a lead-out g from the center tap j.

I contemplate the employment of any suitable type of speaker, whether of a permanent or electrically-energized magnetic type, as well as the employment of suitable conventional vacuum tube ampliers, if greater volume is needed for a large hall or auditorium. The input of an ordinary amplier circuit may be coupled to the terminals c and d of any of the circuits shown.

In Figure 18, I have shown a further embodiment of my invention wherein a unitary button B" is provided having means for adjusting the tension-setting of the electric contact portions of each of its circular diaphragms 83 and 83". In this arrangement, 88 indicates a rectangular housing for the button or pick-up, which like the previously described pick-ups, may be mounted on the tone arm I9 by positioning it between side walls thereof and by employing a setscrew extending through its front inclined face to threadably engage the pick-up housing. In constructing this device, the pick-up housing 80 may be cast or formed in any suitable manner to provide a hollow internal chamber therein adapted to receive conductive granules or particles 8l. An insulating secondary housing 82 of rubber or other suitable material has an outer rectangular shape, see Figure 19, such that it can be slid into the rectangular bore of the housing 8l) from its open top end. The secondary housing 82 carries a pair of insulating retainer rings 82a and 82a for holding outer rim edge portions of the diaphragm 83 and 83 in position therewithin. It will be noted that the diaphragms are positioned in a spacedapart, opposed relationship with respect to each other at their upper rim edges by the rings 82a and 82a' and that they are insulated from the` housing 8|) and its lid or cap 85. The lid 85 of rectangular shape frictionally ts Within the upper or open end 86 of the housing 8D and may be secured in position by solder or upset lug portions 81. Connections a and a are made, as shown, to the two diaphragms 83 and 83' and their insulated leads extend upwardly through `a center hole 88 in the lid 85. The common electrical contact bis made to the housing 80.

Each diaphragm is provided with a bowed-in, centrally-odset, electric contact portion 83a or 83a that integrally carries an axially-outwardlyextending hammer portion 92 or 92. The hollow inner end of the hammer portion 82 or 92' carries a mounting stud portion of an insulated sleeve 89 or 89 that encloses a tension spring 90 or 90', as well as an inner end of an insulating or plastic adjustment screw 9i or 9i'. The

screws 9| and 9 I are provided with male threadsv which engage internal threads through annular mounting parts 88a and 80a. of the side walls of the housing 88 to adjust the tension of their associated springs to thus select the return force action of the diaphragms 83 and 83'. It will be noted that the mounting parts 80a and 80a are '7 screw-threaded into openings in side wall portions of the housing and are centrally-offset to provide electric contacts in axial alignment with the contact portions 83a and 83a of the diaphragms.

In assembling this type of pick-up, the diaphragms, 83 and 83 are positioned within the secondary housing 82, the rings.82a and 82a. are then pushed in from opposite sides of the housing to hold the diaphragms in position therein, and the secondary housing with its diaphragm assembly, is introduced through the open end 86 and mounted in the pick-up housing SG. The conductive particles or granules may then be poured into the housing 8l! from its top or openend 85, through holes 34 and 84 in the housing 32 and holes 84a. and Sila. in the retainer rings, until the requisite level is obtained. Then the leads a and a are threaded through the hole 88 in the lid 85, and the lid is secured in position in the open-end 86 by lugs 81 to tightly position the assembly ina mounted relationship. At this time, the setscrews 9i and 9| may be adjusted to provide any desired or requisite spring tension upon each of the diaphragms electric contact portions through their respective hammer portions.

As compared to a crystal pick-up which generates about one volt, my pick-up acts as a relay and can employ higher voltages, although I prefer to employ a source of current at about 2 to Li1/2 or 5 volts, depending on the wattage output of the speaker coil used. An output of about 1.8 watts to a speaker coil is highly satisfactory, as excess wattage goes into heat.

If a one tube amplier is connected to output contact points c and d of a circuit arrangement such as disclosed, it will produce a volume equivalent to a multiple tube amplier with a crystal pick-up circuit. Frequency variation in the order of l0 cycles can also be obtained with a high of over 15,000 cycles, as compared to the more limited range of a crystal pick-up. A much simplii'led and less expansive circuit arrangement may be used with superior results, as compared to the crystal type of pick-up. The current consumption is so low that ordinary dry cell batteries can be used although, of course, this does not preclude the use of any other suitable source of current, such as may be provided by a half or full wave copper oxide or other type of rectier, employing ordinary household A. C. current. Diaphragms of paper-like thickness are suitable, e. g., about .003 to .005 inch in thickness. The thickness of the diaphragm partially determines the frequency response and I prefer to provide it with a flexibility such that it will return to its zero position within a relatively small fraction of a second. I have found that a yoke element of a thickness of .005 and a width of le" at its neck portion made of phosphorus bronze strip material is satisfactory.

I have determined that the diaphragm must be sensitive to the relatively minute vibrations of the oscillator arm, but must, at the same time, be capable of returning to its zero or starting position. The diaphragm in such return should not over-travel or hunt Since I have shown that the oscillator arm must be in operative association with the diaphragm to effectively transmit movement variations or vibrations thereto, in the preferred embodiment of my invention, I employ a yoke element having a somewhat independent return action, in order that the full force required for the return movement need not be lsupplied entirely by diaphragm action. That is,

a'yoke element may be employed inaccordance with my vinvention to provide a return force action on Vthe oscillator arm sufficient to return the oscillator arm at a proper rate with respect to the return of a previously-deflected diaphragm. vIn this manner, the return force exerted upon the diaphragm Aneed only be suicient to return the diaphragm, itself, although theproportioning of the flexibility of the diaphragmand the yoke maybe eiected in such a manner that the diaphragm 'will provide a. greater force action than-the yoke. The particular proportioning will depend upon desired operating conditions.

In additionv to the other advantages of em- 'ploying a pairof opposed buttons or resistance elements, I'have found that the opposed forces Kexerted by the diaphragms of such elements provide maximum assurance against over-travel and hunting vThat is, the tension force of each diaphragm, exerted through the oscillator arm positioned between opposed diaphragms, normally tends lto balance-out the tension force of the other opposed diaphragm to substantially prevent over-travel or hunting action.

A yoke element can be employed to provide greater fidelity in a pick-up. Tha-t is, the diaphragms can be made of much thinner or more 'sensitive thickness material and have a smaller vinherent lspring or return force action when a ilexibly-rigid'yoke element is employed to provide at least a portion of ythe return force action and -to apply it to the oscillator arm, itself. It

will be noted from the previous description of exemplary :embodiments of my invention that the oscillator arm, although held in contact with the diaphragm hammer portions, is not connected thereto as an integral part thereof, and thus, that the movement-producing action of the vibration ltransmitting oscillator arm is only positive in one direction as applied 4to one diaphragm and .is only positive in an opposite direction as 'applied to the other diaphragm.

4requires-a minimum of equipment, and can be employed in connection with a simple and inexpensive lform of circuit arrangement without the need for any yarnplication. That is, a pick-up .constructed in .accordance with my invention provides superior iidelity, tone quality, and `a faithfulness of reproduction which heretofore could .only be approached by a relatively expensive installation. I feel that I have provided an "al1-purpose type of pick-up which is superior -tin :its 'operative characteristics. vrstable land 'has a high resistance to moisture `as It is highly vcompared to the crystal type of pick-up. Its conductive particles are sealed within the button housings, and its exposed parts or elements can :bemade of moisture-proof materials.

What I claim is:

.1. .An improved electrical pick-up device which comprises, 1an electrical resistance having relatively loosely-positioned, pressure-sensitive-con ductive portions; .a contact Wall in an electrical contacting relationship with the .conductive portions of one side of said resistance; a pressureapplying flexible diaphragm having a Contact portion one side of said contact portion .being in an electrical contacting relationship with the conductive portions of an opposite side of said resistance; said flexible diaphragm having a. portion operably connected with said contact portion to normally urge said contact `portion in a direction away from the conductive portions of the opposite side of said resistance; an actuating means; aflexibly-compressible dampening buffer of comparatively soft material having the physical properties of a solid operably positioned between said actuating means and an opposite side of said contact portion; and said actuating means being in an operative pressure contact .through said dampening buffer with the opposite side of said contact .portion to move the one side of said portion towards the conductive portions of said resistance and compress the conductive portions between said contact portion and said contact Wall.

2. An electrical piclaup device as dened in claim 1 wherein, said dampening buiTer is of water-prooi wool plush material.

3. An electrical pickup device as dened in claim 1 wherein, a housing is positioned to mount the device, said actuating means is operably positioned for oscillation on said housing, and a flexible yoke is opera-bly carried by said housing and is operably connected to said actuating means to return said actua-ting means to a starting' position.

4. An improvedelectrical pick-up device which comprises, an electrical resistance having relatively loosely-positioned, pressure-sensitive, conduotive portions; a contact wall in an electrical contacting relationship| with the conductive portions of one side of said resistance; a pressiueapplying means provided with an electrical contact portion and a hammer portion extending therefrom; said electrical contact portion being in eieotrical contacting relationship with the conductive portions o1" an opposite side of said resistance; said pressure-applying' means being adapted to normally move said electrical contact portion away from the conductive portions of said resistance; an actuating means; a dampening buffer of comparatively soft material having the physical properties of a solid positioned between said actuating means and said hammer portion; and said actuating means being in operable pressure Contact with said hammer portion through said dampening buffer to move said electrical contact portion towards the conductive portions of said resistance and compress the conductive portions between said electrical contact portion and said contact wall.

5, An improved electrical pick-up device which comprises, an electrical resistance provided with loosely-positioned, pressure-sensitive-conductive portions; a pressure-applying means having an electrical contact portion that is centrally-inwardly offset towards and in an electrical contacting relationship with a localized area of one side of the conductive portions of said resistance; said pressure-applying means being of flexible construction to normally urge said contact portion away from .the conductive portions of said resistance; a contact wall in a spaced-apart relation with respect Yto said contact portion, said contact wall havinga contactportion thatis centrally-inwardly:onset towards and 'in substantial axial alignment with said mst-mentioned contact portion; said second-mentioned contact portion being in electrical contacting relationship with a substantially opposite localized area of the conductive portions of said resistance, and an actuating means operably connected to said pressure-applying means to move said rstmen tioned contact portion towards the conductive portions of said resistance to compress them against said second-mentioned contact portion and vary the electrical conductivity of said resistance.

6. An improved electrical pick-up device as dened in claim wherein, a nexible means is operably connected to said actuating means to dampen out undesirable movement of said pressure-applying means.

`'7. An improved electrical converter pick-up device which comprises, a pair of opposed and spaced-apart electrical resistances; each of said resistances having compressible, loosely-positioned, pressure-sensitive-conductive portions; pressure-applying and diaphragm means having contact portions centrally-offset towards and in an operative and electrical contacting relationship with the conductive portions of each of said resistances; said pressure-applying and diaphragm means having oiset flexible portions connected to normallyT urge said contact portions away from the conductive portions of said resistance; contact walls in an electrical contacting relationship with the conductive portions of each of said resistances and having contact portions centrally-oilset away from the conductive portions of said resistances thatare connected to said first-mentioned contact portions through the conductive portions of said resistances; and an oscillating-actuating means operably connected to said pressure-applying means to move said rst-mentioned contact portions alternately in opposite directions toward said opposed resistances and compress their conductive portions.

8. An improved electrical converter pick-up device which comprises, a pair of opposed and spaced-apart electrical resistances; each of said resistances having compressible, loosely-positioned, pressure-sensitive-conductive portions; pressure-applying means having contact portions centrally-offset towards and in an operative and,

electrical contacting relationship with the conductive portions of each of said resistances; said pressure-applying means having iiexible portions connected to normally urge said contact portions away from the conductive portions of said resistances; contact walls in an electrical contacting relationship with the conductive portions of each of said resistances and connected to said contact pertions through the conductive portions of said resistances; an oscillating actuating means operably connected to said pressure-applying means to move said contact portions alternately in opposite directions toward said opposed resistances and compress their conductive portions; and a iiexible self-centering means operatively connected to said oscillating-actuating means. y

9. An improved electrical converter pick-up device which comprises, a pair of opposed and spaced-apart electrical resistances; each oi said resistances being provided with compressible, loosely-positioned, pressure-sensitive, relatively small conductive particles; a pair of pressureapplying diaphragms; each of said diaphragms having axially-centrally located and oppositelyextending hammer and contact portions;v the contact portion of each of said diaphragms being offset towards the conductive particles and away from the hammer portion thereof to receive said hammer portion one of said contact portions being in an electrical contacting-relationship with the localized area of the conductive particles of one oi said resistances and the other of said contact portions being in an electrical contacting relationship with a localized area of the conductive particles of the other of said pair of resistances; each of said pressureapplying diaphragms being of relatively thin, iiexible construction to normally urge its said contact portion away from the conductive portions of the applicable one of said resistances; a contact wall in an electrical contacting relationship with an opposite, localized area of the conductive particles of each of said resistances; and an oscillating element operably mounted in pressure engagement between said hammer portions to move said diaphragms alternately towards the conductive particles of each of said resistances and compress them. t

10. An improved electrical converter pick-up device which comprises, a pair of opposed and spaced-apart electrical resistances; each of said resistances being provided with compressible, loosely-positioned, pressure-sensitive, relatively small conductive particles; a pair of pressure-applying diaphragms; each of said diaphragms having axially-centrally located and oppositelyextending hammer and contact portions; one of said contact portions being in an electrical contacting relationship with a localized area of the conductive particles of one of said resistances and the other of said contact portions being in an electrical contacting relationship with'a 1ocalized area of the conductive particles of the other of said pair of resistances; each of said pressure-applying diaphragms being of relatively thin, exible construction to normally urge its said contact portion away from the conductive portions of the applicable one of said resistances; a contact wall in an electrical contacting relationship with an opposite, localized area of the vconductive particles of each of said resistances;

an oscillating element operably mounted in pressure engagement between said hammer portions to move said diaphragms alternately towards the conductive particles of each of said resistances and compress them; and a flexible means operatively connected to said oscillating element to normally urge it away from said pressure-diaphragms toward a substantially central position with respect thereto.

11. An improved electrical converter pick-up device which comprises, a pair of opposed and spaced-apart electrical resistances; each of said resistances being provided with compressible, loosely-positioned, pressure-sensitive, relatively small conductive particles; a pair of pressure-applying diaphragms; each of said diaphragms having axially-centrally located and oppositelyextending hammer and contact portions; one of said contact portions being in an electrical contacting relationship with a localized area of the conductive particles of one of said resistances and the other of said contact portions being in an electrical contacting relationship with a localized `area of the conductive particles of the other of said pair of resistances; each of said pressure-applying diaphragms being of relatively thin, flexible construction to normally urge its said contact portion away from the conductive portions of the applicable one of said resistances;

a contact wall in an electrical contacting relationship with an opposite, localized area of the conductive particles of each of said resistances; an oscillating element operably mounted in pressure engagement between said `hammer portions to move said diaphragms'alte'rnately towards the conductive particles of each of said resistances and compress them; and a dampening buffer of comparatively soft material having the physical properties of a solid positioned between the hammer portion of each of said diaphragms and said oscillating element.

12. An improved electrical pick-up device which comprises, an integral housing defining a hollow chamber of relatively narrow thickness that extends radially and is open to one side thereof; said housing having a back wall opposite to the open side thereof; relatively ne carbon particles normally loosely enclosed within the hollow chamber of said housing; a flexible diaphragm mounted over the open side of said housing and in a compressible relationship with respect to said back wall; said diaphragm having a centrally-located contact portion in an electrical contacting relationship with said carbon particles; said back wall having a contact in substantial alignment with the contact portion of said diaphragm and in an electrical contacting relationship with said carbon particles; said diaphragm having a exible annular oiTset portion adjacent its outer periphery to normally flex said contact portion away from said carbcn particles; and an oscillating means operably connected to said contact portion to move it towards said back wall contact and compress said carbon particles.

13. An improved electrical pick-up device which comprises, an oscillator arm provided with a stylus holder; an electrical resistance having pressure sensitive, electric current conductive particles; a flexible diaphragm having a contact portion in an electrical contacting engagement with said conductive particles; a hammer portion extending substantially axially outwardly from the electrical contact portion of said diaphragm; said oscillator arm being operably connected to the hammer portion of said diaphragm to impart stylus variations to said diaphragm and move said contact portion into a compressing relationship with said conductive particles; and a spring element operably carried by said diaphragm connected to said diaphragm to normally urge said contact portion away from said conductive particles.

14. An improved electrical pick-up device which comprises, an oscillator arm provided with a stylus holder; an electrical resistance having pressure sensitive, electric current conductive particles; a flexible diaphragm having a contact portion in an electrical contacting engagement with said conductive particles; a hammer portion extending substantially axially outwardly from the electrical contact portion of said diaphragm; said oscillator arm being operably connected to the hammer portion of said diaphragm to impart stylus variations to said diaphragm and move said contact portion into a compressing relationship with said conductive particles; a spring element operably connected to said diaphragm to normally urge said contact portion away from said conductive particles; and said spring element being adjustably mounted with respect to said diaphragm.

15. An improved electrical pick-up device for translating tracery of a record or tape which comprises, an oscillating arm provided with a stylus holder adjacent one end thereof, an electrical resistance having pressure-sensitive-electrically-conductive particles, a flexible diaphragm member in operative: engagement with said conductive particles, said diaphragm member being operably positioned in a relatively noncompressing relationship with respect to said conductive particles, means adjacent thevother end of said oscillating arm operably connecting said oscillating arm to said diaphragm member, said oscillator arm being fulcrumed between its end portions to transmit stylus variations to said diaphragm member and move it toward said conductive particles, and flexible means operably connected to the other end of said oscillator arm to return it to a starting position.

16. A pick-up device as defined in claim 15 wherein, said iiexible means is a metal yoke, a housing positions the pick-up device, and said metal yoke is operably connected between said housing and said oscillating arm.

17. An improved electrical pick-up device for translating record tracery which comprises, an oscillating arm having a stylus holder for following tracery variations, a fulcrum resiliently mounting said oscillator arm to amplify the tracery variations; an electrical resistance having conductive, pressure-sensitive particles; a nexible metal diaphragm in an operative electrical contacting relationship with the particles of said resistance, a fabric dampening buier operably positioned between said oscillating arm and said diaphragm, said diaphragm being actuated by said oscillating arm to move it towards the particles of said resistance, said diaphragm having ilexible portions providing a maximum sensitivity to positive movement of said oscillating arm in a direction toward said diaphragm to move said diaphragm away from the particles of said resistance when the force of a positive movement of said oscillating arm is withdrawn.

18. A resistance unit pick-up that comprises, a housing, a pair of resistance unit halves positioned in an opposed spaced-apart relationship within said housing, each of said resistance unit halves having a back wall portion and an opposed exible diaphragm in a spaced-apart relationship with respect to each other, relatively minute carbon granules positioned in the spacing between said back wall portion and said diaphragm of each of said halves, said diaphragms being in an opposed and spaced-apart relationship with respect to each other, an oscillator arm, a fulcrum operably mounting said oscillator arm on said housing, said oscillator arm being mounted by said fulcrum to extend along the spacing between said diaphragms, said oscillator arm having a stylus holder at one end thereof and a pair of opposed face portions at its other end substantially centrally engaging said diaphragms, said oscillator arm being adapted to move each of said diaphragms toward the back wall portion of its corresponding unit half to compress said carbon granules in accordance with variations imparted by said stylus holder, each of said diaphragms having means for urging it away from said carbon granules to a starting position, and a iiexible yoke mounted on said housing and operably connected to the other end of said oscillator arm to urge said oscillator arm towards a neutral position between said diaphragms.

JOSEPH H. MCKNIGHT.

(References on following page) REFERENCES CITED UNITED STATES PATENTS Number Name Dat v1,176,577 yLee Mar. 21, 1916 1,281,565 Haub Oct. 15, 1918 1,564,290 Smith Dec. 8, 1925 -1,570,662 Wyatt Jan. 26, 1926 1,656,424 Cover Jan. 17, 1928 Perkins Jan. 17, 1928 Number Number Name Date Burch May 29, 1928 Ruben May 6, 1930 Matthias Jan. 16, 1934 Engholm Nov. 4, 1941 Scherbatskoy Aug. 29, 1944 Courcy Jan. 23, 1945 Cook Mar. 23, 1945 Root Oct. 14, 1947 FOREIGN PATENTS Country .Y Date Great Britain ,May 1, 1930 

